Studies concerning the hormonal and metabolic regulation of amino acid metabolism in tissues of the rat will be continued. Of particular interest is the regulation of the oxidation of the branched chain amino acids, in skeletal and heart muscle, blood vessels, retina, nerves and parenquimal organs. The regulation of branched chain amino acid metabolism is being studied in control and diabetic animals and in other catabolic states. The interrelationship between the oxidation of different substrates by muscle, protein turnover and the shift from negative to positive N2 balance is being investigated. Studies concerning the effect of hormones (insulin glucagon, cortisol, catecholamines, GH) on the oxidation of branched chain amino acids, amino acid release, protein synthesis and degradation are in progress. The branched chain alpha-keto dehydrogenase system appears to be the rate limiting step in branched chain amino acid oxidation by muscles. Differences in regulation between muscles and other tissues have been reported. The cellular mechanism by which these systems are regulated is being investigated. Studies concerning the role of isoleucine and leucine as precursors of lipids in certain tissues are being continued, especially with regard to the effect of diabetes.